WO2011004226A2

WO2011004226A2 - Wastewater treatment tank

Info

Publication number: WO2011004226A2
Application number: PCT/IB2010/001500
Authority: WO
Inventors: Mario Vitarelli
Original assignee: Zetaplast S.P.A.
Priority date: 2009-06-19
Filing date: 2010-06-21
Publication date: 2011-01-13
Also published as: ITPI20090078A1; WO2011004226A3

Abstract

A tank (1) for wastewater treatment comprises a first treatment chamber (11), in which the waste water, or sewage, is fed through an inlet duct (12). In the first treatment chamber (11), the waste water is subject to a physical treatment for separating it into a first fraction (101) having a high concentration in solid particles, which is deposited mainly on the bottom (15) of the chamber (11), and in a second fraction (102) at high concentration of the liquid part, lighter, which is rises, instead, above the first fraction (101) up to a certain height from the bottom (15). In a first exemplary embodiment, the tank (1) comprises, furthermore, a second treatment chamber in which the liquid fraction (102) of the waste water is supplied, for example through a transfer duct (50), for being subject to a following treatment that causes the production of a clarified liquid fraction (102') drawn through an outlet (24). The clarification of the liquid fraction (102) in the second treatment chamber (21) is effected by a separation means (150) comprising at least one membrane of tubular shape (151) having an outer surface (152) equipped with a plurality of pores (156) of measured size. The, or each, membrane of tubular shape (151) is arranged in a vertical position in the treatment chamber.

Description

TITLE

WASTEWATER TREATMENT TANK DESCRIPTION

Field of the invention

The present invention relates to the field of wastewater treatment and it relates, in particular to a wastewater treatment tank for sewage coming from the toilets and from the kitchens of public, or private buildings, i.e. both waste water of household origin, and waste water coming from buildings, or installations, where it is carry out commercial activities, or for manufacturing goods, but in any case comparable waters, according to law, to waste water of household origin.

Description of the prior art

As well known, household sewage is normally disposed of through the sewer system. If this is not possible, according to law, the waste water must be treated before the introduction in a receiving body.

The most common is the Imhoff treatment that performs a mechanical sedimentation and an anaerobic degradation of the sludge that has to be disposed of. Typically an Imhoff tank comprises an upper compartment for sedimentation of the sewage and a lower compartment for storage and anaerobic digestion of the settled sludge. The two compartments are separated by one, or more dividing walls having slits that allow the two compartments to communicate with each other.

The solid sludge present in the waste water passes through the communication slits from the sedimentation compartment into the storage and digestion compartment located underneath where the anaerobic fermentation is obtained. In the lower compartment an anaerobic degradation is carried out of the settled sludge that after the digestion is accumulated at the bottom from which it is periodically removed.

However, the water that is withdrawn from the Imhoff tank are clarified, but still rich of not depurated putrescible material present in higher amount than the limits according to law such that they cannot be directly disposed of to irrigate the soil, or dispersed in surface water bodies water surface.

To overcome this drawback depuration plants exist of biological type where the degradation of the polluting substances, in particular substances containing carbon, phosphorus and nitrogen, is obtained by bringing the sewage to depurate with a mass of particular microorganisms called "sludge-active" that can decompose the pollutants present in waste water and convert them into a biomass. The biological process can be carried out in the presence of oxygen, where aerobic biological oxidation is involved, or without oxygen, where degradation or anaerobic fermentation is involved.

The biological treatment processes are characterized by high depuration efficiency, a variable time for completing the degradation process of the substances, and a starting investment that is less expensive in case of anaerobic systems with respect to plants involved with aerobic processes . The plants based on aerobic processes require in most cases the use of apparatus less bulky but provide higher installation costs, higher energy supply and a higher operation cost .

As previously said degradation of the pollutants is obtained by an aerobic digestion carried out by bacteria present in the sewage same. The air insufflation speeds up this process up to the production of particular bacterial colonies, so-called activated sludge. An index often used for evaluating the level of polluting a mass of water is the BOD5 (Biochemical Oxygen Demand 5-day test) responsive to the amount of oxygen necessary to oxidize some substances contained in the water by the aerobic microorganisms. It is therefore an indirect measure of the bacteriologically degradable organic substances present in the water.

In KR20020072082 a wastewater treatment tank is described comprising a plurality of treatment chambers. More precisely, the wastewater treatment tank comprises a first settling chamber, a flow equalization chamber, three aeration chambers, a second settling chamber, a filtration chamber, a separation chamber and a microfiltration chamber. Therefore, the microfiltration chamber is arranged downstream of a plurality treatment chambers that perform a progressive clarification of the waste water that is introduced in the tank. In fact, in the separation chamber modules are mounted having follow fibres oriented horizontally. Therefore, it is necessary to achieve a high clarification level of the waste water before introducing it in the separation chamber, in order to avoid the contamination of the hollow fibre modules.

However, this depuration system, like other similar systems, in addition to resulting extremely disadvantageous concerning costs, is structurally complex, and requires a continuous and periodic maintenance, since a bad operation of a single chamber jeopardizes the correct operation of the whole tank.

Furthermore, the tank above described has a low ratio between the amount of clarified waste water and the treatment volume. Furthermore, also the transportation and installation in loco of the tank is troublesome since it has having at least 7-8 treatment chambers. Summary of the invention

It is therefore a feature of the present invention to provide a wastewater treatment tank, in particular waste water of household origin and comparable waters, which provides a high depuration efficiency.

It is also a feature of the present invention to provide a wastewater treatment tank that is capable of treating even high amount of waste water and that is at the same time easily portable.

It is another feature of the present invention to provide a wastewater treatment tank that overcomes the difficulties of the depuration apparatus of the prior art.

It is a particular feature of the present invention to provide a wastewater treatment tank that provides a high clarification of treated waste water for reducing the number of intermediate treatments with respect to similar solutions of the prior art.

These and other features are accomplished with one exemplary wastewater treatment tank, in particular waste water of household origin, or comparable waters, according to the present invention, said tank comprising:

- at least a first hollow tank body having at least one inlet and defining a first treatment chamber, in said first treatment chamber a separation by settling occurring of waste water fed through said inlet, obtaining a solid fraction, which is deposited mainly on the bottom of the first chamber, and a liquid fraction, which rises in the first chamber up to a certain height;

- at least a second hollow tank body defining a second treatment chamber, said second hollow tank body being operatively connected to said first hollow tank body, said second treatment chamber being in hydraulic connection with said first treatment chamber through at least one opening, in said second chamber occurring the clarification of waste water coming from said first chamber through said opening, said second hollow tank body comprising at least one outlet for extracting waste water that has been clarified in said second chamber;

- wherein between said second treatment chamber and said outlet a separation means is arranged comprising at least one permeable membrane, said separation means adapted to separate by said membrane the waste water liquid fraction present in said second chamber from particles having size larger than pores of said permeable membrane;

whose main feature is that said, or each, permeable membrane has tubular shape, said, or each, permeable membrane having an outer surface and having at least one open end connected to a suction duct communicating with said outlet, in order to cause the waste water liquid fraction to clarify to pass from the outside into the membrane of tubular shape, and then to be subjected to suction via the suction duct, whereas the solid particles of size larger than the pores do not cross the membrane of tubular shape and remain therefore out of it, and that said, or each, membrane of tubular shape is arranged according to a vertical position, such that the particles that are on the outer surface of the membrane of tubular shape detach and precipitate towards the bottom of said second treatment chamber.

Advantageously, the membrane of tubular shape is made of flexible material .

For example, the membrane of tubular shape is a "hose" net .

In particular, a means can be provided for insufflating air bubbles into said second treatment chamber. More in detail, the air bubbles cause the membrane of tubular shape to shake and a detachment from the outer surface of the membrane of tubular shape of the solid particles that do not pass the pores.

Advantageously, a means is provided for reversing momentarily the clarified water flow by the suction duct in the membrane in order to cause a flow from the inside to the outside of the membrane of tubular shape. More precisely, the temporary inversion of flow causes the membrane of tubular shape to shake and a detachment from the outer surface of the membrane of tubular shape of the solid particles that do not pass the pores.

In particular, the means for reversing momentarily the clarified water flow from the inside to the outside of the membrane of tubular shape can reverse the flow repeatedly after regular periods. For example, a control means can be provided that is adapted to operating, repeatedly after regular periods, the inversion of the flow by the means for reversing momentarily the flow.

In particular, the regular periods are comprised between 10 minutes and 2 hours.

Advantageously, the regular periods are comprised between 15 minutes and 1 hour.

Advantageously, a pump means is provided acting in the second treatment chamber, said pump means adapted_to pump a washing fluid out of said, or each, membrane of tubular shape. More in detail, the washing fluid causes a detachment from the outer surface of the membrane of tubular shape of the solid particles that do not pass the pores .

In particular, the separation means can be a microfiltration separation means, in particular said microfiltration separation means adapted to separate the liquid fraction from the particles having size larger than 1.5 micron, advantageously, larger than 0.1 micron.

In addition, or alternatively, the separation means can be ultrafiltration separation means, in particular said ultrafiltration separation means adapted to separate the liquid fraction from the particles having size larger than 0.1 micron, advantageously, larger than 0.005 micron.

In addition, or alternatively, the separation means can be a nanofiltration separation means, said nanofiltration separation means adapted to separate the liquid fraction from the particles having size larger than 0.005 micron, advantageously, larger than 0.001 micron.

In addition, or alternatively, the separation means can be a separation means by reverse osmosis, said reverse osmosis separation means adapted to separate the liquid fraction from the particles and from the substances with different chemical affinity such as minerals, colloids and bacteria in it present;

In particular, the microfiltration, ultrafiltration, nanofiltration and reverse osmosis separation means comprises a respectively: a selectively permeable, or semipermeable, membrane unit having membranes for microfiltration, ultrafiltration, nanofiltration and reverse osmosis, respectively, that are in hydraulic connection with each other.

In particular, the selectively permeable, or semipermeable, membranes, for microfiltration, ultrafiltration, nanofiltration and reverse osmosis of each membrane unit are arranged according to a predetermined array comprising a predetermined number of rows and columns of membranes .

In particular, each of said separation means comprises a at least one permeable membrane that is adapted to separate the second treatment chamber forming a first region in which the waste water liquid fraction to clarify is present and a second region in which the clarified waste water liquid fraction is present, i.e. the fraction without particles having size larger than the pores of the membrane.

In particular, the second region is in hydraulic connection through said outlet with a means to provide a pressure difference (ΔP) between the first and the second region in order to cause the movement of the liquid fraction to treat through the membrane.

In particular, the pressure difference created between the first and the second region by the means to provide a pressure difference (ΔP) can be set between 2 bar and 0.1 bar, advantageously between 1.5 bar and 0.2 bar, preferably between 1 bar and 0.3 bar.

Advantageously, the means to provide a pressure difference (ΔP) between the first and the second region of the second chamber comprises a pump means adapted to pick up, through said outlet, the clarified liquid fraction from the second region of the second chamber and to discharge it into a storage container.

In case of nanofiltration separation means, or reverse osmosis separation means, advantageously, an additional pump means is provided, said additional pump means is adapted to feed the liquid fraction to treat to said nanofiltration separation means, or in said reverse osmosis separation means, respectively, at a predetermined pressure P_Oi.

In particular, the pressure can be set between 2 bar and 70 bar.

Advantageously, the pressure is set between 3 bar and 40 bar .

Advantageously, the separation means comprises a plurality of semipermeable membranes arranged in series in order to be crossed in turn by said flow of said liquid fraction to treat.

Advantageously, the plurality of semipermeable membranes are arranged in order to have a decreasing nominal size of the pores following the direction of the flow of the liquid fraction which crosses it.

Preferably, the plurality of semipermeable membranes arranged in series have a different nominal size of the pores. More precisely, said membrane of tubular shape of said plurality of membranes arranged in series have a decreasing nominal size of the pores following the direction of the flow of the liquid fraction which crosses it. This way, the flow of the liquid fraction crosses firstly the membrane, or the membrane unit, which provides a less fine depuration and, then the membrane, or the membrane unit, which achieves a finer depuration. Therefore, from the liquid fraction through the series of membrane the particles are removed in turn having size gradually decreasing size.

Advantageously, the second treatment chamber has an discharge spillover outlet. This way, in case of absence of electric energy the liquid fraction to treat is withdrawn through a discharge duct connected to discharge spillover outlet avoiding that it can pollute the clarified liquid fraction.

Advantageously, the tank, according to the invention, comprises, furthermore, at least one third hollow tank body defining a third chamber in hydraulic connection with said first and/or with said second treatment chamber.

In particular, the third hollow tank body can be arranged upstream of the second hollow tank body for being in hydraulic connection with the second region of the second treatment chamber with function of container for collecting clarified waste water.

In an exemplary embodiment, the third hollow tank body is arranged between the first and the second hollow tank body. In this case, in the third hollow tank body a third treatment chamber can be provided for example for biologically treating the liquid fraction.

In particular, in the clarified waste water liquid fraction at the outlet of the second chamber the particles have size less than 1.5 micron, advantageously, particles having size less than 0.1 micron, preferably particles having size less than 0.001 micron.

In particular, in the second treatment chamber the liquid fraction can be subject to a biological treatment, in particular a biological treatment of aerobic type carried out by aerobic microorganisms.

In particular, in the second treatment chamber at least one filling body is added that is adapted to increase the contact surface between the waste water liquid fraction and the aerobic microorganisms.

Advantageously, in the second treatment chamber a plurality of filling bodies is added forming a filling body.

Advantageously, said, or each, filling body is of floating type, said, or each, filling body floating in said liquid fraction present in said second treatment chamber in order to form a mobile floating bed. More in detail, the, or each, filling body has a behaviour like an "ice cube". Therefore, in case of a plurality of filling bodies in the second chamber different layers are formed more or less homogeneous of filling bodies at different heights from the bottom of the second chamber.

In particular, the separation means can be associated with a protection means arranged in use between said separation means and said, or each, filling body, said protection means adapted to avoid that said, or each, filling body can hit against said separation means. This way, it is avoided that the filling bodies can hit against the separation means and damage them jeopardizing the correct operation of the tank, according to the invention, and, in particular, the depuration efficiency.

For example, the protection means comprises at least one tubular body arranged, in use, between the separation means and said, or each, filling body, said tubular body covering at least in part said separation means.

In an exemplary embodiment, the tubular body can cover completely the separation means in order to define a treatment basin in hydraulic connection with the second treatment chamber through at least one opening.

Advantageously, the treatment basin is contained at least partially in the second treatment chamber.

Advantageously, the treatment basin is completely contained within the second treatment chamber. In this case, the treatment chamber provides at least one opening arranged below the separation means in order to cause the sludge products to move by gravity from the third to the second treatment chamber .

In another exemplary embodiment of the invention the protection means have a reticular structure, or grid structure, in order to avoid the impact of the, or each, tubular body against the separation means, allowing in the meantime the liquid fraction to treat to reach the separation means.

In particular, a means can be provided for removing the solid particles deposited on the surface of the separation means which faces towards the first region.

Advantageously, the means for removing comprises a means for delivering a washing liquid, said means for delivering acting in the first region of the second treatment chamber.

In an exemplary embodiment , the means for removing comprises a means for delivering a washing liquid acting in the second region of the second treatment chamber. In this case, the washing liquid can coincide with the clarified liquid fraction.

In particular, the pump means for pumping said clarified liquid fraction from said second region to said storage container can be of reversible type. In this case, the pump means of reversible type take, for example periodically, the clarified liquid fraction from the storage container to pump it through the separation means.

Advantageously, a means is provided for reversing the flow of said pump means .

In particular, in the second treatment chamber can act oxygen diffusion means, for example a membrane diffusion means, in order to assist the production of masses of aerobic microorganisms, or "activated sludge". They absorb the pollutants contained in the waste water and eliminate them in the form of simple compounds.

Advantageously, the first and the second treatment chambers are put in communication with a duct comprising:

- a first portion arranged in the first treatment chamber and equipped with at least one inlet opening;

- a second portion arranged in the second treatment chamber and equipped with at least one outlet .

Advantageously, the connection duct of the first and of the second treatment chambers can be in hydraulic connection with a pump, for example housed in a containing recess, for pumping, in particular in conditions of high flow of waste water entering the first treatment chamber, the waste water treated in the first chamber into the second chamber. In particular, the inlet opening can be arranged at a height from the base of the first chamber more than half its height, advantageously, more than 2/3 of its height.

Advantageously, the second portion of the duct has a plurality of exit apertures. In particular, the apertures of said plurality are arranged in a substantial uniform way along the second portion of the duct .

In particular, the second portion of the duct is arranged near to, or next to, the basis of the second treatment chamber.

In particular, two successive hollow tank bodies can be connected to each other in succession by means of respective flanged portions.

Advantageously, two successive hollow tank bodies are separated by a wall equipped with at least one opening that is adapted to put in hydraulic connection the respective treatment chambers.

In particular, each hollow tank body can be made of a single part of plastic material by moulding, in particular a rotational moulding process.

Preferably, the oxygen diffusion means comprises at least one insufflating compressor. In particular, the insufflating compressor is associated with a timer that adjusts the oxygen to supply in the second treatment chamber. More in detail, the amount of oxygen to supply is adjusted responsive to the type of use to let aerobic bacteria to carry out a full oxidation of the organic material and to make the process highly efficient.

In particular, the insufflating compressor is of the type with a membrane that is adapted to optimize the tightness and the energy consumption.

Preferably, each hollow tank body is made of thermoplastic polymer material selected from the group comprised of: polyethylene, polypropylene, PVC, polyamide, polycarbonate, polyurethane, PET, which can be mixed at moulding or overlapped in layers with reinforcing agent such as: foams, fibres, charge.

Advantageously, each hollow tank body is made of a single part .

In particular, the side surface of each hollow tank body can be equipped with a plurality of circumferential ribs adapted to provide a corrugated surface that increases the rate of structural stiffness. This feature is particularly relevant when the tank, according to the invention, is used as a tank embedded in earth.

In particular, each treatment chamber can be obtained fixing several hollow tank bodies to each other and leaving in communication with each other in order to form a single treatment chamber having a high capacity.

In particular, the open end of the membrane can be connected to a suction duct, in order to cause the fraction of waste water to clarify to pass from the outside into the hose, and then sucked away, whereas the solid particles that have a size not capable of crossing the hose remain out of the hose .

In an exemplary embodiment of the invention, the separation means comprises a plurality of membranes of tubular shape arranged in parallel. More in detail, a collection element is provided in communication with each membrane of tubular shape, said collection element is in communication with said outlet.

Brief description of the drawings

Further characteristic and the advantages of the wastewater treatment tank, according to the present invention will be made clearer with the following description of an exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings in which:

- figure 1 diagrammatically shows a longitudinal sectional view of a wastewater treatment tank, according to the invention;

- figure 2 diagrammatically shows a perspective view of a partial cross section of an exemplary embodiment of the wastewater treatment tank of Fig. 1;

- figure 3 shows in detail the membrane used to carry out the clarification of waste water by the tank of Fig. 1;

- figure 4 shows a perspective view of a membrane unit used to carry out the clarification of waste water by the tank of Fig. 1;

- figure 5 shows for example a possible arrangement of more groups of membranes used for clarifying the waste water contained in the tank of Fig. 1;

- figures from 6 to 8 show in detail some exemplary embodiments of the second treatment chamber of the invention;

- figure 9A diagrammatically shows an exemplary embodiment of the invention with the means for washing the membrane of Fig. 3 ;

- figure 9B diagrammatically shows an alternative exemplary embodiment of the means for washing the membrane of Fig. 9A;

- figures from 10 to 15 show some exemplary embodiments of the invention for the tank of Fig. 1;

- figure 16 shows an exemplary embodiment of the invention with the separation means.

Description of a preferred exemplary embodiment

With reference to Fig. 1, a tank 1, according to the present invention, for wastewater treatment, in particular waste water of household or civil origin, comprises a first treatment chamber 11, in which the waste water, or sewage, is fed through an inlet duct 12. In first treatment chamber 11, the waste water is subject to a treatment physical for separating them into a first portion 101 having a high concentration of solid particles, which are deposited mainly on the bottom 15 of chamber 11, and in a second portion 102 with a high liquid fraction, lighter, which rises, instead, above fraction 101 up to a certain height from base 15.

In a first exemplary embodiment, tank 1 comprises, furthermore, a second treatment chamber in which liquid fraction 102 of the waste water is supplied, for example through a transfer duct 50, for being subject to a treatment that causes the production of a clarified liquid fraction 102' drawn through an outlet 24.

As shown in detail in Fig. 3, transfer duct 50 comprises, in particular, a first portion 51 arranged in first treatment chamber 11 and equipped with at least one opening 53, for example arranged on the facing flange, through which fraction 102 enters duct 50, and a second portion 52 arranged in second treatment chamber 21 equipped with at least one outlet 54 through which the fraction 102 comes out from duct 50.

To avoid that in duct 50 floating waste can enter, such as residues of oils, greases, detergents, etc. present on the free surface of the mass of the sewage, opening 53 is arranged at a height Hl from base 15 suitable for remaining below the liquid surface of the mass of waste water, but above solid fraction 101. For example, the height Hl can be more than half the total height H of chamber 11. Furthermore, portion 51 of duct 50 can be equipped with filters, or grids, not shown in the figure, to avoid that solid waste can pass inside coming from first treatment chamber 11. First and second treatment chambers 11 and 21 can be separated by a wall 40 and can communicate via transfer duct 50 passing through an opening 45 made in the wall 40.

As diagrammaticalIy shown in Fig. 2, in addition, or alternatively, to duct 50 the movement of the liquid fraction from first chamber 11 to second chamber 21 can is operated by a pump 17 arranged in a recess 18 made in first treatment chamber 11. This exemplary embodiment is particularly advantageous for transferring waste water from first chamber 11 to second treatment chamber 21 in case high inlet flows of sewage into tank 1. In case of such high flow rate, in fact, are created turbulent motion may be present in the mass of waste water present in first treatment chamber 11 that can jeopardize the correct operation of the same.

Second treatment chamber 21 is, furthermore, equipped with a discharge spillover outlet 26. This way, in case of absence of electric energy, liquid fraction 102 to treat can be discharged through a duct connected to discharge spillover outlet 26 avoiding that it can pollute clarified liquid fraction 102'.

According to the invention, the clarification of liquid fraction 102 in second treatment chamber 21 is effected by a separation means 150 comprising at least one membrane of tubular shape 151 having an outer surface 152 equipped with a plurality of pores 156 of measured size. The, or each, membrane of tubular shape 151 is arranged in a vertical position in the treatment chamber.

In particular, each membrane 151 can be a flexible tube for example a "hose" of a very fine net, i.e. equipped with pores of a size equal to, or less than, about 1.5 micron. More precisely, each permeable membrane 151 can be of semipermeable type, i.e. is a membrane that allows only to certain molecules to cross it. Each membrane of tubular shape 151 has at least one open end at which it is connected to a suction duct. This way, the waste water passes from the outside into the membrane of tubular shape 151, or hose, and then is subjected to suction. The solid particles of size not capable of crossing hose 151 remain out of the same.

The fact that the membranes of tubular shape 151 are arranged in vertical allows the particles that deposit on the outer surface of the hose detaching by gravity and depositing on the bottom of second treatment chamber 21. A detachment of the particles from the outer surface 152 of membrane 151 can be obtained causing the membrane of tubular shape to shake for example by air bubbles insufflated into said second chamber, or by temporarily reversing the flow of the liquid fraction, as described in detail hereinafter.

More precisely, as diagrammatically shown in Fig. 3, each permeable membrane 151 separates second treatment chamber 21 into a first region 21a, in which liquid fraction 102 to treat is present, and in a second region 21b, in which the clarified liquid fraction 102' is present. The latter fraction, owing to the action of the membrane 151, is free, with respect to liquid fraction 102 to treat, of particles 155' having size larger than pores 156 of membrane 151 and then not capable of passing into region 21b.

In particular, a means is provided 180 to cause a pressure difference (ΔP) between first region 21a, in which in operation conditions a pressure Pl is present, and second region 21b in which in operation conditions a pressure P2<P1 is present, in order to cause a forced passage of the liquid fraction to treat 102 through membrane 151 and obtain, then, its clarification. The means to provide the pressure difference (ΔP) comprises, for example, a centrifugal pump 185 that in normal operation draws the clarified liquid fraction 102' from region 21b and feeds it into a storage container 110. The pressure difference created between the regions 21a and 21b can be comprised, for example, between 2 and 0.1 bar, advantageously between 1.5 and 0.2 bar, preferably between 1 bar and 0.3 bar .

Separation means 150 can be selected according to the needs and, in particular, to desired clarification rate. More precisely, in case of a rough clarification, a microfiltration separation means 150a can be used, capable for removing from liquid fraction 102 the particles of size larger than about 1.5 micron, up to 0.1 micron, according to the type of microfiltration membrane used. In the case, instead, of a medium clarification an ultrafiltration separation means 150b can be used, for capable for removing from liquid fraction 102 the particles of size larger than about 0.001 micron, up to 0.005 micron. Further, to provide a clarification much more precise, for separating particles with size larger than 0.001 micron instead, nanofiltration can be used as separation means 150c.

Finally, for separating the liquid fraction to treat 102 from particles 155 such as minerals, colloids and bacteria in it present reverse osmosis separation means 15Od can be advantageously used (Fig. 16) . In this case, liquid fraction 102 that can be prefiltered through at least one of separation means 150a-150c previously described, is supplied at high pressure by a pump 190 in a modular portion 15Od for carrying out reverse osmosis. The high pressure, for example set between 3 and 60 bar, to which liquid fraction 102 is supplied into modular portion 15Od achieves a clarification according to a process known obtaining a clarified liquid that is, then, supplied to storage tank 110 by a duct 302, and a concentrated sludge that is, instead, discharged by a duct 301.

In a further exemplary embodiment, the clarified solution, before being put in storage tank 110, can be subject to a purification and/or remineralization treatment. This can be obtained causing the clarified water to pass through a fixed packed bed 350 of dolomite, or of mineral salts, or a combination thereof.

As diagrammaticalIy shown in Fig. 4, each separation means 150 can comprise a support portion 155 that is adapted to support a membrane unit 151 of the same type, i.e. a microfiltration, or ultrafiltration, or nanofiltration membrane, or still a membrane for reverse osmosis. Membranes 151 of a same unit are in hydraulic connection with each other and are arranged in a predetermined array comprising a predetermined number of rows (i) , for example 3 rows (i=3) , and a predetermined number of columns (j), for example 3 columns (j=3) , for a total of 9 membranes 151, (in Fig. each membrane 151ij is identified according to the number of the relevant row (i) and column (J)).

In an exemplary embodiment, as diagrammaticalIy shown in Fig. 5, it is possible to arrange in series several separation means 150 of different type. More in detail, the order in which separation means 150 are arranged, and then crossed by the flow of liquid portion 102, is responsive to the size of the pores 156 of membrane 151. More in detail, separation means 150 are arranged in series so that the flow of liquid fraction 102 to treat crosses firstly separation means 150, which performs a more or less rough clarification and then those that perform a harder clarification. For example, liquid fraction 102 that is present in second treatment chamber 21 can cross firstly microfiltration separation means 150a, then may cross ultrafiltration separation means 150b and finally may cross the nanofiltration separation means 150c obtaining a highly clarified liquid fraction 102'.

In an exemplary embodiment of the invention, but not shown in the figures, it is possible, furthermore, to arrange in parallel several separation means 150 as above described, both of the same type and of different type.

In a preferred exemplary embodiment of the invention, shown for example in Fig. 6, in second treatment chamber 21 liquid fraction 102 is subject to a biological treatment owing to aerobic microorganisms . In this case, the portion 52 of duct 50 can be arranged, in use, at bottom 25 of second chamber 21, or close to it, in such a way that liquid fraction 102 remains in chamber 21 for a certain time before reaching separation means 150.

More precisely, in second treatment chamber 21 oxygen diffusion means are present, for example a membrane diffusion means 85. This feeds a predetermined amount of oxygen in chamber 21 in order to assist the production of masses of aerobic microorganisms, or "activated sludge" which absorb the pollutants contained in the waste water and eliminate them in the form of simple compounds.

An increase of contact surface between liquid fraction 102 and aerobic microorganisms, in second treatment chamber 21 can be obtained arranging a certain number of filling bodies 70.

In this case, as shown in Fig. 7, separation means 150 are associated with a protection means 170 arranged in use between separation means 150 and filling bodies 70. In particular, protection means 170 are adapted to avoid that the filling bodies 70 hit against separation means 150 and damage them. In the exemplary embodiment shown in Fig. 7, protection means 170 comprises a plurality of raschig rings 171 arranged, in use, about separation means 150.

In an exemplary embodiment shown in Fig. 8, protection means 170 covers completely separation means 150 and defines a treatment basin 22 in hydraulic connection with second treatment chamber 21 through at least one opening 74. The treatment basin 22 is contained at least partially in second treatment chamber 21 and has at least one opening 75 arranged below separation means 150 in order to cause particles 155, which cannot cross membrane 151 to fall by gravity down to second treatment chamber 21. Container 170, which defines treatment basin 22 is enclosed at least in part in container 62, which defines the second treatment chamber 21.

In another exemplary embodiment of the invention, not shown in the figures, protection means 150 consists of a cage of plastic material, or of metal, in which separation means 150 are arranged. More precisely, the meshes of the cage grid are smaller of the filling bodies 70 that therefore cannot contact separation means 150.

For removing the layer of particles that do not pass through membrane 151 and that adhere to its external surface, a means for removing is provided acting in first region 21a, or in second region 21b, and is adapted to remove the particles stuck to the surface of membrane 151 that faces towards first region 21a. More in detail, the means for removing is adapted to release a pressurized fluid against the external surface, or internal, of membrane 151 for causing it to a shaking and then the fall of the material stuck to the external surface.

In the exemplary embodiment diagrammatically shown in Figs. 9A and 9B, the cleaning fluid can coincide with the clarified liquid fraction 102' . In this case, the pump means 180 described with reference to Fig. 3, can be of reversible type. More precisely, the pump means 180 of reversible type are associated with a set of valves 181-183, or 181-184, capable of providing both a flow of the clarified fraction 102' from second region 21b towards the storage container 110, and a flow in an opposite direction, i.e. from the storage container 110 to second region 21b. For example, repeatedly after regular periods, it is possible to work on valves 181-183, or 181-184 taking the clarified liquid fraction 102' from storage container 110 to pump against separation means 150 from second region 21b to cause a counter-washing of membrane 151.

In the case shown in Fig. 9A, the pump means 180 comprise three valves 181-183 controlled by a control unit 200. This operates valves 181-183 in order to provide a flow of clarified liquid fraction 102 from second region 21b to storage tank 110 (Fig. 3) , or an opposite flow of clarified liquid fraction 102, i.e. from storage tank 110 to second region 21b.

In the case of Fig. 9B, instead, the pump means 180 comprises four three-way valves 181-184 that are suitably connected and selectively operated in order to reverse the direction of the flow of the clarified liquid fraction 102' in order to make it possible to take it from storage tank 110 for feeding it into region 21b.

As shown, for example in Figs. 1 and 2, tank 1 is of modular type and comprises at least a first and a second hollow tank bodies 61 and 62, connected to respective flanged portions 65 and 66 for example by means of bolts, or thermoplastic welding, or other similar systems. More precisely, modular tank 1 comprises at least one first hollow tank body 61 in which first treatment chamber 11 is defined and a second hollow tank body 62 in which second treatment chamber 21 is contained.

More precisely, modular tank 1 can comprise only hollow bodies modular 61 and 62 (Figs. 1, 2, 10 and 11) , in this case it comprises only the first and the second treatment chambers 11 and 21, which may have a substantially equivalent capacity, or different, as shown in Fig. 10. The higher capacity of the treatment chamber 21 increases the time of treatment of liquid fraction 102 to obtain, then, a finer clarification. In this case, to ensure a homogeneous distribution of liquid fraction 102 into the volume of the chamber 21, the portion 52 of transfer duct 50 can be equipped with an additional portion, or extension element.

Each hollow tank body 61, 62 is preferably obtained in a single piece by a rotational moulding process. Furthermore, tank 1 can be equipped peripherally of ribs 90 in order to augment remarkably the mechanical stiffness.

In an exemplary embodiment of the invention, tank 1 can comprise a number of modular hollow bodies larger than two. For example, as shown in Figs. 12 and 13, tank 1 can comprise three hollow tank bodies 61, 62 and 61', or a number even larger of modular hollow bodies, according to the capacity demand for which the specific application which the clarified liquid fraction 102' is intended. In this case, as shown in Fig. 13, a means is provided 175 for picking up the sludge deposited on the bottom of second chamber 21 and feed them back to the first treatment chamber biological of tank 1.

In particular, in tank 1 an additional treatment chamber 21' is provided in which a preliminary biological treatment is carried out of liquid fraction 102 before discharging it into second treatment chamber 21. In this case, the adjacent treatment chambers 61, 61' and 61' ,62, are separated by dividing walls 40' and 40 and are put in communication with a duct 50 having a first and a second portion 51 and 52, where first portion 51 is arranged at a predetermined height Hl from the base of the starting chamber 61, or 62', and the portion 52 laying on, or near to, the bottom of the arrival chamber 62 ',o 62.

As shown still in Fig. 14, a hollow tank body 69 can also be provided for collecting the clarified water at the outlet of treatment basin 22.

In addition, or alternatively, to hollow tank body 69, the treatment basin 22 of tank 1 can be in communication with a collection container 110 out of tank 1, in which the clarified water is gathered and then drawn when needed for being sent to users to it connected.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims

- 1 - CLAIMS

1. Wastewater treatment tank, in particular waste water of household origin or comparable waters, said tank comprising:

- at least a first hollow tank body having at least one inlet and defining a first treatment chamber, in said first treatment chamber a separation by- settling occurring of waste water fed through said inlet, obtaining a solid fraction, which is deposited mainly on the bottom of the first chamber, and a liquid fraction, which rises in the first chamber up to a certain height;

- at least a second hollow tank body defining a second treatment chamber said second hollow tank body being operatively connected to said first hollow tank body, said second treatment chamber being in hydraulic connection with said first treatment chamber through at least one opening, in said second chamber occurring the clarification of waste water coming from said first chamber through said opening, said second hollow tank body comprising at least one outlet for extracting waste water that has been clarified in said second chamber;

characterised in that said, or each, permeable membrane has tubular shape, said permeable membrane having an outer surface and having at least one open end connected to a suction duct communicating with said outlet, in order to cause the liquid fraction - 2 - of said waste water to clarify to pass from the outside into said membrane of tubular shape, and then to be subjected to suction via said suction duct, whereas the solid particles of size larger than said pores do not cross said membrane of tubular shape and remain therefore out of it;

and that said, or each, membrane of tubular shape is arranged in a vertical position, such that the particles that deposit out of said membrane of tubular shape detach and precipitate towards the bottom of said second treatment chamber.

2. Wastewater treatment tank, according to claim 1, wherein said membrane of tubular shape is flexible .

3. Wastewater treatment tank, according to claim 1, wherein said membrane of tubular shape is a "hose" net .

4. Wastewater treatment tank, according to claim 1, wherein a means is provided for insufflating air bubbles in said second treatment chamber, said air bubbles causing a shaking of said membrane of tubular shape and a detachment of said solid particles that do not pass said pores from the outer surface of said membrane of tubular shape.

5. Wastewater treatment tank, according to claim 1, wherein a means is provided for reversing momentarily the flow of said water clarified by said suction duct in said membrane in order to cause a flow from the inside to the outside of said membrane of tubular shape, said temporary inversion of flow causing a shaking action of said membrane of tubular shape and a detachment of said solid particles that do not pass said pores from the outer surface of said membrane of tubular shape.

6. Wastewater treatment tank, according to claim 5, wherein said means for reversing momentarily the flow - 3 - of said clarified water from the inside to the outside of said membrane of tubular shape reverse said flow repeatedly after regular periods.

7. Wastewater treatment tank, according to claim 6, wherein said regular periods are comprised between 10 minutes and 2 hours, advantageously they are comprised between 15 minutes and 1 hour.

8. Wastewater treatment tank, according to claim 1, wherein a pump means is provided acting in said second treatment chamber, said pump means adapted to pump a washing fluid out of said, or each, membrane of tubular shape and a detachment of said solid particles that do not pass said pores from the outer surface of said membrane of tubular shape .

9. Wastewater treatment tank, according to claim 1, wherein said separation means comprises a microfiltration separation means adapted to separate the liquid fraction from the particles having size larger than 1.5 micron, advantageously, larger than 0.1 micron.

10. Wastewater treatment tank, according to claim 1, wherein said separation means comprises a ultrafiltration separation means adapted to separate the liquid fraction from the particles having size larger than 0.1 micron, advantageously, larger than 0.005 micron.

11. Wastewater treatment tank, according to claim 1, wherein said separation means comprises a nanofiltration separation means adapted to separate the liquid fraction from the particles having size larger than 0.005 micron, advantageously, larger than 0.001 micron.

12. Wastewater treatment tank, according to claim 1, - 4 - wherein said separation means comprises a reverse osmosis separation means that is adapted to separate the liquid fraction from the particles and from the substances with different chemical affinity such as minerals, colloids and bacteria in it present.

13. Wastewater treatment tank, according to claim 1, wherein said membrane separates said second chamber in a first and in a second region, said second region being in hydraulic connection through said outlet with a means to provide a pressure difference (ΔP) between said first and said second region in order to cause the movement of said liquid fraction to treat through said membrane .

14. Wastewater treatment tank, according to claim 13, wherein said means to provide said pressure difference (ΔP) between said first^' and said second region of said second treatment chamber comprises a pump means adapted to take through said outlet said clarified liquid fraction from said second region and to discharge it into a storage container.

15. Wastewater treatment tank, according to claim 1, wherein in said second treatment chamber said liquid fraction is subject to a biological treatment, in particular a biological treatment of aerobic type carried out by aerobic microorganisms, in particular, by air insufflation.

16. Wastewater treatment tank, according to claim 15, where in said second treatment chamber at least one filling body is added that is adapted to increase the contact surface between said liquid fraction and said aerobic microorganisms .

17. Wastewater treatment tank, according to claim 16, wherein said, or each, filling body is of floating type, said, or each, filling body adapted to float in - 5 - said liquid fraction present in said second treatment chamber in order to form a mobile floating bed.

18. Wastewater treatment tank, according to claim 1, wherein said separation means comprises a plurality of permeable membrane arranged in hydraulic connection in series, said membrane of said series being crossed in turn by said flow of said liquid fraction to treat.

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19. Wastewater treatment tank, according to claim 18, wherein said membranes of tubular shape of said plurality of membranes arranged in series have a decreasing nominal size of the pores following the direction of the flow of the liquid fraction which crosses it .

20. Wastewater treatment tank, according to claim 16, wherein said separation means is associated with a protection means arranged, in use, between said separation means and said, or each, filling body, said protection means adapted to avoid that said, or each, filling body can hit against said separation means and damage them.

21. Wastewater treatment tank, according to claim 1, wherein, furthermore, at least one third hollow tank body is provided defining a third chamber, said third chamber being in hydraulic connection with at least one among said first and said second treatment chamber.

22. Wastewater treatment tank, according to claim 1, wherein a plurality provides membrane of tubular shape arranged parallel and a collection element is provided in communication with each hose, said collection element being in communication with said outlet.